Wednesday, 2 April 2014

Ideal pH

The ideal pH for passivity of metals in heating systems

If layers have formed on the metals in the heating system and
if they are stable the metal becomes passive to corrosion and oxygen attacks.
Thus this process is called passivation or passivity of metals.

The picture shows the pH ranges for common metals in heating
systems when these react with passivation or corrosion.

The pH for aluminium is said to be 4-9 but it is better to
create a buffer, most common is a limitation of 8.5.

The pH-range of 8.2 to 8.5 in heating
systems in the presence of aluminium is only a compromise. As you can see the
stability of iron starts at a pH of 9.﻿